The invention relates to a method of recording and/or reproducing a picture signal and an associated audio signal in/from a record carrier, in which during recording the picture signal and the audio signal are encoded to form a first and a second information signal respectively comprising information words arranged in frames, each frame comprising a frame header and a data field, a data field of a frame comprising a plurality of information words of the picture signal or an audio signal, the header indicating the information signal to which the information words in the data field belongs, after which the frames are recorded on the record carrier; and in which during reproduction the frames are read from the record carrier and are decoded to obtain the picture signal and the associated audio signal. The invention also relates to an apparatus for carrying out the method and to a record carrier obtained by means of the method. A method of the type defined in the opening sentence is described in the Applicant's previous Netherlands patent application No. 8,600,450. More in particular, the invention relates to a method of recording and reproducing picture signals and associated audio signals in the form of digital information in/from a record carrier, such as for example, a compact disc.
As is generally known, tne compact disc is a record carrier for the storage of digital information, which record carrier can contain a specific number of bits. The first application of the compact disc in the Compact Disc Digital Audio System, which is already a few years old envisaged its use as a record carrier for 16-bit PCM-encoded audio signals. For a comprehensive description of this system reference is made to Philips' Technical Review, Vol. 40, 1982, No. 6, in particular the article by J. P. J. Heemskerk et al entitled "Compact disc system aspects and modulation," pages 157 to 164.
A second application envisaged its use as a data ROM for data-processing equipment. A third application which is now being developed and envisages its use as a record carrier for digitized video signals of pictures accompanied by digital audio signals and, if desired, computer data.
The application of the compact disc now envisaged is an interactive use, referred to as "CD-I". Papers on this novel use have already been read at the Micro-soft Conference in Seattle, 3-5 Mar. 1986, namely a paper by D. C. Geest entitled "Standardization of CD-I" and a paper by R. Bruno entitled "New developments in optical media," which was published in the "Philips Koerier" of Mar. 13, 1986, pages 1 and 2.
In order to enable a picture to be recorded on a record carrier of the compact-disc type, the picture is divided into a plurality of lines (for example 280 lines) and every line is divided into a plurality of contiguous picture elements(for example 384 elements). It is assumed that each picture element is of uniform brightness and uniform colour. A picture element can be defined completely by a number of picture components; namely the luminance component Y(i,k) and the two colour-difference components U(i,k) and V(i,k) or, which is in principle the same, by the three basic colour components R(i,k), G(i,k) and B(i,k). Here i is the sequence number of the line and k the sequence number of the picture element on this line (column).
Each of the picture components of a picture element is subjected to a coding, so that for each picture element an information word is obtained, hereinafter referred to as "video word". If PCM coding is applied the picture components of each picture element are encoded separately, i.e. independently of corresponding picture components of other picture elements. However, if the picture components are subjected to a DPCM coding, broadly speaking only the difference between the corresponding picture components of every two successive picture elements is subjected to a PCM coding. Since encoding such a difference generally requires a smaller number of bits than separately encoding each of the picture components, DPCM encoding is applied for each of the picture components in the envisaged new application of the compact disc. This means that each picture elexent is characterized by a 12-bit video word.
For a most economic use of the capacity of the record carrier the entire block of 280.times.384 video words is transmitted only once. The monitor comprises a picture memory having a number of storage locations which is at least equal to the number of picture elements in the picture. Each storage location is unambiguously associated with a picture element and such a storage location contains the transmitted video word of the relevant picture element. This picture memory is read out repeatedly in the customary manner in order to display the relevant picture.
It is to be noted that in practice it is not found to be necessary to transmit both the luminance component and the two colour-difference components of each picture element. It is found to be satisfactory to transmit the luminance contents of each picture element and alternately the colour-difference component U and the colour-difference component V of successive picture elements. This means that each picture element can be characterized by an 8-bit video word. More in particular, the first four bits of this video word represent the luminance component of the picture element in DPCM format and the four other bits represent (alternately) one of the two colour-difference components, also in DPCM format. Hereinafter, the totality of video words to be transmitted, which together define a specific picture, will be referred to as a "video block".
In the novel application of the compact disc now envisaged, a video block is arranged in frames prior to recording on the record carrier, similarly to the digitized information components, audio and computer data. Each frame comprises, for example, 2352 bytes and each frame is roughly divided into two fields, namely a frame header comprising 24 bytes and a data field of 2328 bytes. The last 280 bytes in the data field may be used for error protection and error correction of the other bytes in the data field. This is utilized, for example, if the frame contains computer data.
The frame header inter alia comprises synchronization bytes for byte and bit synchronization, but also indicates whether the data in the data field is picture information, audio information or computer data. These cases are referred to as a video frame, an audio frame and a computerdata frame respectively. The data field of an audio frame comprises 1164 audio words of 16 bits each, while the data field of a video frame comprises 2328 video words of 8 bits each.
The novel use of the compact disc now envisaged moreover provides the possibility of choosing from a number of different audio-signal qualities.
Firstly, there is the quality known from the original use in the Compact Disc Digital Audio system. This results in compact disc fully packed with audio signals providing approximately 72 minutes of stereo sound of the well-known compact-disc quality (a dynamic range of 90 dB or better).
Secondly, there is the "hifi music" mode. This possibility provides two stereo channels which are reproducible parallel to each other or four mono channels which are reproducible parallel to each other. A full compact disc then provides approximately 72 minutes of sound per stereo channel. Thus, if on a compact disc only one monosignal should be recorded, it is possible to store 4.times.72 minutes of audio signal on a full compact disc. The quality corresponds to that of a conventional long-play record.
Thirdly, there is the "midfi music" mode. In this case a full compact disc contains four parallel channels, each channel accommodating a stereo signal of 72 minutes length, or eight channels containing a mono signal of 72 minutes length. The quality corresponds to that of an FM radio transmission.
A fourth possibility is the "speech" mode. This mode provides 8 parallel channels of stereo or 16 parallel channels of mono signal of maximum 72 minutes length on a full compact disc. The quality is the same as that of an AM radio transmission.
As is known, CD digital audio is encoded in accordance with a 16-bit PCM code and the full storage capacity of the compact disc is necessary for the storage bit of the 72-minute stereo signal.
The three other qualities with which the audio signal can be recorded on the record carrier are realized by means of an 8-bit or 4-bit ADPCM code (adaptive data pulse code modulation).
These three possibilities require a storage capacity of 50%, 25% and 12.5% for the storage of the audio information of one channel. The remainder of the storage capacity is then available for the storage of video information, computer data or for other sound channels. In the last-mentioned case it is possible to store speech in different languages in a corresponding number of parallel channels.
A fifth possibility is to encode the speech phonetically, so that an even longer playing time can be obtained. The standard phonetic alphabet as specified for the desired lenguage or languages is encoded and recorded on the compact disc together with a set of diphones for the desired language and a resynthesis program by means of which the speech can be resynthesized by joining the diphones to each other. The resulting information density in one channel can be very high and may result in a playing time of over 5000 hours for one full compact disc.
In those cases in which two or more parallel channels are available it is possible, as stated previously, to store the same speech translated in different languages in these channels on the compact disc. This is of particular importance when simultaneously reproducing picture information and associated speech, to provide a possibility of selecting the language in which said speech is to be reproduced.